The Internal Ribosome Entry Site of Dengue Virus mRNA Is Active When Cap-Dependent Translation Initiation Is Inhibited

ABSTRACT

Dengue virus (DENV) is an enveloped, positive-sense, single-stranded RNA virus belonging to the Flaviviridae family. Translation initiation of DENV mRNA can occur by a cap-dependent or a cap-independent mechanism. Two non-mutually exclusive cap-independent mechanisms of translation initiation have been described for DENV mRNA. The first corresponds to a 5′-end-dependent, internal ribosome entry site (IRES)-independent mechanism, while the second relies on IRES-dependent initiation. In this report, we study the recently discovered DENV IRES. The results show that the DENV IRES is functional in the rabbit reticulocyte lysate (RRL). In accordance, the activity of the DENV IRES was resistant to the cleavage of eukaryotic initiation factor 4G (eIF4G) by the Foot-and-mouth disease virus leader protease in RRL. In cells, the DENV IRES exhibited only marginal activity under standard culture conditions. The DENV IRES showed weak activity in HEK 293T cells; however, DENV IRES activity was significantly enhanced in HEK 293T cells expressing Human rhinovirus 2A protease. These findings suggest that the DENV IRES enables viral protein synthesis under conditions that suppress canonical translation initiation.

IMPORTANCE Dengue virus (DENV), the etiological agent of dengue, a febrile and hemorrhagic disease, infects millions of people per year in tropical and subtropical countries. When infecting cells, DENV induces stress conditions known to inhibit canonical protein synthesis. Under these conditions, DENV mRNA thrives using noncanonical modes of translation initiation. In this study, we characterize the mechanism dependent on an internal ribosome entry site (IRES). Here, we describe the activity of the DENV IRES in vitro and cells. We show that in cells, the DENV IRES enables the viral mRNA to translate under conditions that suppress canonical translation initiation.